A Category Under Strain

[A] Ecology divides species into those that belong in a place and those that have been brought to it, and the division does more work than it can support. [B] A species counts as native if it was present at some chosen date, and the date is chosen for reasons that have little to do with ecology: the beginning of written records, the arrival of a particular people, the retreat of the last ice. [C] Move the date and the membership changes. [D]

The difficulty is not merely one of bookkeeping. The word carries a judgement as well as a description, and the two are not always earned together. Most introduced species do nothing at all; a small number cause damage that is severe and well documented; and a few that arrived long enough ago to be counted as native behave in every way like the ones being removed. A policy that follows the category rather than the behaviour will spend money on a harmless plant because of its passport and leave an aggressive one alone because of its own. None of this is an argument for indifference to what arrives. It is an argument for describing what a species does, and for keeping that description separate from the question of where it came from.